This application has a specification in common with application Ser. No. 956,551 filed Oct. 30, 1978 and assigned to the common assignee.
Electric melt furnaces are well known in the art, as are apparatus and methods for starting an electric glass melting furnace.
A known system is shown in U.S. Pat. No. 3,842,180. In that patent, parallel electrodes are shown entering the bottom wall of the furnace. The electrodes are arranged in groups, preferably groups of three. During start-up, when the material is cooled and the resistance is high, as in the case of glass having a negative resistance coefficient, hot spots must be created and a high source of energy applied to the melt. In this case, as shown in the prior art patent, each of the three electrodes within a single group is operated from a different phase of a polyphase power supply. The current then passes between each of the electrodes of a single group. Since the electrodes are close together, the resistive path between the electrodes permits the flow of current, even though the material to be melted is cool and its resistance high.
After a time, when the material has started to warm up and has reached operating temperature, each of the electrodes within a group is switched to operate off the same power supply in parallel, and a current path is created between that group of electrodes and a similar group of three electrodes which are also connected in parallel to the power supply. As in the first group of electrodes, the second group of electrodes is operated during the cool period of the furnace, with each of the electrodes within the second group connected to a separate phase of the power supply.
The electrodes shown within the prior art are typically parallel, generally entering the bottom of the furnace or the side of the furnace, and with a constant displacement maintained between the parallel electrodes.
The disadvantage of such prior art arrangement is that leakage occurred between the electrodes all along the length of the electrodes, and the parallel electrodes were unable to maximize the energy at the tips of the elctrodes or to direct the maximum energy to a particular area of the furnace. Overall, this increased wear and tear on the walls, as excessive energy flowed around the electrodes about the walls, and directed excessive heat in portions of the furnace where the material was already melted and heated to a hot state, and where the additional heat was unnecessary.
The prior art shows electric furnaces for melting glass wherein the electrodes are convergent with respect to each other. One such example is shown in U.S. Pat. No. 2,267,537 issued Dec. 23, 1941. In that patent, convergent electrodes are shown mounted in the side wall of the furnace for placing the greatest amount of heat along the center line of the furnace. In addition, divergent electrodes are used for placing the maximum amount of heat along the sidewalls of the furnace to counteract the heat losses along the sidewalls. Other examples of the prior art show various modifications of electrodes inserted into a furnace at various angles with respect to each other. These prior art patents include: U.S. Pat. No. 3,374,211 wherein the electrodes are placed divergently; U.S. Pat. Nos. 3,145,246 and 3,147,328 where the electrodes enter the walls of the circular furnace and are spaced farther apart than at the tips; and U.S. Pat. No. 3,725,558.
However, it is believed that the prior art does not show two sets of electrodes: a group of inclined electrodes and a separate set of parallel electrodes. Further, the function of these electrodes and the interaction between these two groups is not known: That is a group of inclined electrodes connected to create a current path with a parallel electrode and wherein a switching means is provided for selectively energizing the inclined elctrodes operated as a group separately energizing the inclined electrodes and a parallel electrode to create a current path between the inclined electrode group and parallel electrode.